This invention relates to an improved bipolar transistor of a multi-emitter construction.
In conventional transistors of the type described, many emitter diffusion layers are formed in a base diffusion layer, and an emitter electrode is formed on each emitter diffusion layer. Such transistor is equivalent to a structure in which many transistors are arranged in parallel. With this construction, a uniform base current can be supplied to the surface of each emitter diffusion layer, and therefore the effective area of the emitter as a whole can be close to the geometric area. This achieves an increased maximum operating current of the transistor.
However, in such a conventional transistor, when the base current increases, a voltage drop due to the resistance of a base electrode film occurs during the time when the base current flows through the base electrode film. Therefore, the magnitude of the base current can not be maintained uniform between the emitter diffusion layer disposed close to the base current supply source and the emitter diffusion layer disposed remote from this supply source. More specifically, when the base current is thus rendered non-uniform, the maximum operating current of the transistor is limited to a magnitude or level determined by the emitter diffusion layer subjected to a large base current (that is, having a large emitter current) among the emitter diffusion layers. This results in a problem that the maximum operating current of the transistor is smaller than the sum of the maximum operating currents of the emitter diffusion layers.
Under the above circumstances, for example, in the case where a specified one out of the emitter diffusion layers is used as a transistor for detecting the total emitter current, the relation of proportion between the detection current detected by such detection transistor and the total emitter current becomes improper when a large current flows, which results in a problem that the detection of the total emitter current can not be accurately carried out, as shown in FIG. 4(b).